Optical Encoders and Laser Interferometers

How minute is your positional change ? Is it angular or linear?

Hello stevem,

I plan to measure the motion of a torsion pendulum. I expect the range to be microns or less. So it is both linear and rotational.

Thanks for replying. jim

Encoder background : http://en.wikipedia.org/wiki/Rotary_encoder

Since your application needs to non-contact you may want to consider using a magnetic encoder or a resolver.

http://www.admotec.com/magnetic_encoders.htm

http://en.wikipedia.org/wiki/Resolver_(electrical)

Any encoder disk whichever design will have an inertia so that if you measure a torsion this inertia will add and may be change the natural frequency. You could use a distance measurement using a triangulation principle which is based on a reflected IR light.The surface of your rotating part has to be reflective.

True, in that case either a capacitive or fiberoptic probe could be used.

http://www.mtiinstruments.com/products/mti2100fotonic.aspx

Before anything can be suggested we will need to know the range, precision and response time required of the application.

Hi,

very good and very sensitive capacitive transducers are made by

Lion-Precision (St.Paul)

Fogale-Nanotech (France)

Micro-Epsilon (Germany)

PI (Germany)

I tested these and had very good results.

Then I made my own ones - much cheaper.

Laser triangulation is not at all near the quality of capacitive sensing for small distances.

RHABE

Call Keyance. They have systems directly designed for this application. I have one that we measure dynamic movement of piezoelectric transducers during actuation in the 0.05 to 25 um @ up to 150 Hz.